The invention relates to a cutting machine, in particular a tread cutting machine, having at least one cutting blade linearly traversable on a blade carriage for achieving a feed movement and rotationally driven by a motor.
DE 38 06 645 C2 discloses a transverse-cutting apparatus for textile webs which has a rotationally driven, disk-shaped cutting blade. The cutting blade is mounted on a blade carriage which is linearly traversable for achieving a feed movement. The motor for the drive of the cutting blade is firmly mounted outside the blade carriage and in relation to the drive is coupled to the cutting blade by a torque-transmission means designed as an endless belt. A further endless belt is provided in order to be able to traverse the blade carriage, and this further endless belt can likewise be driven by a motor arranged outside the blade carriage and is firmly clamped to the blade carriage.
A similar cutting apparatus for cutting foodstuffs has been disclosed by German Utility Model DE 89 04 725.7 U1.
In these apparatuses, the dynamics of the feed movement, compared with the previously conventional arrangement of the motor for the rotational drive of the cutting blade on the blade carriage, are markedly improved, since the mass of the blade carriage is reduced overall.
In the tire industry, cutting apparatuses have been used for many years for the cutting of treads, these cutting apparatuses likewise having a motor-driven cutting blade on a blade carriage traversable transversely to the tread. In this case, however, the drive motor for the cutting blade is arranged on the blade carriage, so that its mass is comparatively large and impairs the dynamics of the feed movement. Under the comparatively rough operating conditions of a tread cutting machine with its high number of stress cycles per year and its high feed rates during the cut and during idle strokes (return travel into the cutting initial position), a type of construction having a drive motor arranged outside the blade carriage leads to high loads on the mechanical drive system, which greatly reduce its service life.
The object of the invention is to improve a cutting machine of the generic type to the effect that a highly dynamic feed movement of the blade carriage is ensured with a long service life of the drive system, in which case the construction outlay required for this is to be comparatively small.
This object is achieved according to the invention by the features specified patent claim 1. Advantageous developments of the invention are specified in the subclaims.
The present invention is based on the knowledge that the mass of the drive system, normally designed as an electric motor, for the rotating cutting blade constitutes the essential determining factor for the total mass of the blade carriage in the hitherto conventional design. The invention breaks away from the idea that the drive motor absolutely has to be arranged on the blade carriage and traversed together with the latter and instead provides for the motor for the blade drive to be arranged outside the blade carriage, i.e. in a fixed position. For the transmission of the torque from the motor to the cutting blade, a torque-transmission means is provided, this torque-transmission means being characterized by the fact that part of the torque-transmission means which has to be traversed with the blade carriage has a markedly lower mass than the motor installed in a fixed position. As a result, a drastic reduction in the total weight of the blade carriage can be achieved. This reduction in weight in turn permits a considerable improvement in the dynamics of the feed movement, since the forces for the acceleration or braking of the blade carriage turn out to be correspondingly markedly lower.
The invention relates to a cutting machine, in particular a tread cutting machine, having at least one cutting blade linearly traversable on a blade carriage for achieving a feed movement and rotationally driven by a motor.
However, it should be taken into account that, during a traverse of the blade carriage in the direction of the movement of the revolving torque-transmission means, a reduction in the drive speed of the cutting blade occurs on account of the superimposed movement, whereas, conversely, during a traverse of the blade carriage against the direction of movement of the revolving torque-transmission means, an increase in the rotational speed of the cutting blade occurs. This variation of the rotational speed lies within a range of up to +/xe2x88x9230% of the rated speed. On the one hand, during the cutting phase, such a change in the rotational speed may lead to losses of quality during the cutting. On the other hand, the forces caused by the braking or acceleration of the rotating blade mean a considerable additional load, which would reduce the service life of the mechanical drive system. The invention therefore provides for the motor for the rotary drive of the cutting blade to be provided with a device which ensures that the rotational speed of the cutting blade is kept at least approximately constant during a feed movement of the cutting blade. This should be ensured in particular when the cutting blade is just in cutting engagement. The rotational speed of the cutting blade is preferably kept completely constant continuously. This can be effected in a particularly simple manner by an actual-value detection of the blade.
Alternatively, instead of a closed-loop speed control, an open-loop control of the blade rotational speed may also be provided, the motor of the blade being controlled as a function of the desired value of the feed rate, the feed direction and the transmission ratio of the toothed belt. In both the case of a closed-loop control and an open-loop control, the invention brings about a drastic reduction in the mechanical loads of the belt drive (e.g. toothed belt) due to the fact that there are no acceleration forces (no variation in the blade rotational speed). This has a considerable effect on the reliability of a trouble-free operation without repairs especially on account of the high number of cutting operations, which is around 7 million pieces/annum for example.
For a cutting operation of high quality, it is often important for the cutting direction to always remain the same. This means that, after a feed movement of a cutting operation, a corresponding idle stroke back into the initial position of the blade carriage regularly has to be effected. So that the material to be cut is not damaged by the idle stroke, provision is advantageously made in a manner known per se for the cutting machine according to the invention to be equipped with a swinging device, by means of which the cutting blade can be brought from the cutting position into a neutral position by a tilting movement, and vice versa. To actuate this swinging device, a hydraulic or pneumatic cylinder system, for example, may be provided. In this case, the tilting movement is effected about an axis which is oriented essentially coaxially to the direction of movement of the torque-transmission means. As a result, only corresponding slight twisting of the torque-transmission means occurs during the tilting, and this twisting can easily be tolerated and neither disturbs the torque transmission nor leads to impairment of the torque-transmission means itself.
In order to be able to adapt the cutting angle to the respective requirements, a setting device for setting the cutting angle of the cutting blade is advantageously provided in a manner likewise known per se, it being possible for this setting device to be likewise operable by a hydraulic or pneumatic cylinder system for example.